**4.5 Effect of digestate on the microbiological activity of soil**

Soil microbial community has an important role in the fertility of soil and its alteration after intervention to the soil (e.g. manuring, soil improving, soil pollution) could be indicate more sensitive these changes than changes in the soil physical and chemical properties.

et al., 2008).

Digestate: A New Nutrient Source – Review 303

sweet corn, silage maize) groups. The sensitive plants can be treated by digestate only in their certain life stages, for example, young alfalfa is very sensitive after sowing while old alfalfa is very sensitive before cutting. In the case of sensitive plants the burning effect of digestate can be observed but it follows a strong and quick recovering process. For the nonsensitive plants the digestate can be used in any developmental stage. It is favourable, because for example, in rainy period the digestate technically could not be applied (Makádi

The right application rate of liquid or solid digestate depends on the plant nitrogen demand. It should be applied when plant N demand arises. This time for non-legume scpecies is the late winter and spring (Stinner et al., 2008). Similarly, Wulf et al. (2006) used 70% of the digestate in spring and 30% in autumn, while Makádi et al. (2008) and Nyord et al. (2008)

Because of its high available nutrient content, digestate application resulted in significantly higher aboveground biomass yields in the case of winter wheat and spring wheat than the farmyard manure and undigested slurry treatment. The effectiveness of a digestate depends on the composition of co-digestied material, the treated plant species and the treatment methodology. Co-digestion of different organic materials results in more effective digestate.

After the burning effect of digestate the soybean plants recovered and grew more, but lower sprouts. These sprouts were very productive, the number of pods was also higher in the treated samples, therefore the yield and thousand seed weight were also higher (Table 7,

> Weight of pods (g m-2)

> > 351.2± 69.69a

> > 521.0± 20.30b

> > 811.0± 33.09c

Table 7. Yield parameters of soybean after digestate treatment (*Data from Makádi et al., 2008).* a, b, c indexes mean the different statistical groups according to Tukey's test (p<0.05).

These yield parameters are close correlations with some soil parameters changing after digestate amendment. Increasing in important nutrient contents contribute to the better

Comparing the effect of liquid digestate and the equal quantity of water to the yield of sweet corn and silage maize, significantly higher yields were found in the digestate treatment. In this case the applied digestate on the bases of plants N demand was split into two parts (Makádi et al., 2006). That means that the favourable effects of digestate are caused by its

Weight of grain (g m-2)

> 233.2± 40.61a

> 335.2± 43.46b

> 566.5± 25.05c

Thousand seed weight (g)

> 134.3± 1.71a

> 172.2± 6.61b

> 191.0± 8.69c

split into two and three the applied rate through the vegetation period.

Weight of sprout (g m-2)

> 218.0± 33.08a

> 214.4± 4.98a

> 234.4± 7.73a

mean±S.D.

development of plants (Makádi et al., 2008b, Table 8).

soluble macro- and micronutrient content.

(Möller et al., 2008; Stinner et al., 2008).

Height of plants (cm)

1.15a

2.68a

7.73a

Makádi et al., 2006)

<sup>0</sup>74.3±

<sup>5</sup>71.8±

<sup>10</sup>70.2±

Digestate (L m-2)

Among the different organic wastes like compost, biogas residue, sewage sludge and different manures with and without mineral N, the biogas residue was more efficient for promoting the soil microbiological activity. The high amount of easy-degradable carbon increased the substrate induced respiration (SIR), which was enhanced by the higher carbon content resulted from the higher litter and root exudates of higher plant growth. In accordance with these results, the largest proportion of active microorganisms was found in the digestate treated samples (Odlare et al., 2008; Kirchmann, 1991). Similarly, the activity of invertase was significantly higher in the digestate treated samples than that in control ones (Makádi et al., 2006).

Besides the macro- and micronutrient content of digestate which are important not for the crops but for soil microorganisms too, it contains growth promoters and hormones, also. Therefore it could be used for stubble remains to facilitate their decomposing. Makádi et al. (2007) compared the effect of digestate and Phylazonit MC bacterial manure on the growth of silage maize (*Zea mays* L. 'Coralba') as a second crop after winter wheat and on the enzyme activities of soil. Digestate was used at the rate of 50% of the total N demand of silage maize while the Phylazonit MC was used at 5 L ha-1 dose. Their results of the changes in enzyme activities are summarized in Table 6.


Table 6. Invertase and catalase activities of soil on the 3rd and 9th week after digestate and Phylazonit MC treatment (*Data from Makádi et al., 2007*). a, b, c indexes mean the different statistical groups according to Tukey's test (p<0.05).

The maximum of the degradation of disaccharides, indicated by the invertase activity, was found in the 3rd week after Phylazonit MC treatment, while it was found only after the 9th week in the digestate treated soil samples. The Phylazonit MC contains only bacteria and promoting agents of bacterial activity for degrading the soil OM. Contrarily, in the digestate treated samples the degradation of disaccharides takes place at similar rate through 9 weeks because of the OM content of digestate used. Changes in catalase activity indicate the effect of nutrient content of digestate to the increasing microbial metabolism.
